Solar heating systems in the past have been completely filled with a collector fluid, except for a small expansion volume in the surge tank.
As I have disclosed in my copending application, Ser. No. 775,731, filed Mar. 9, 1977, the present solar heating system departs from past practice in that a refrigerant, such as the fluorinated hydrocarbons, is used as the collector fluid. Only the collector is filled with liquid refrigerant, the balance of the system containing refrigerant gas according to the pressure-temperature relationship of the refrigerant. Normally, there are no pressure reducing valves or regulating valves used in the system. The entire system being basically under the same pressure, such control devices may be dispensed with. However, this is not to exclude the use of such structure under certain conditions. The pressure will be determined by the condensing temperature in the heat exchange structure.
In past practice the sensible heat of the collector fluid is raised in the collector as heat is picked up. The collector fluid is then circulated by a pump (using some energy) to a heat exchanger or heat dissipating or storing device.
In this invention latent heat of the refrigerant is picked up causing the liquid refrigerant to "boil" and change to vapor according to the amount of heat picked up. Vapor pressure immediately travels to the heat exchange structure where it condenses and returns as a liquid to the collector, this being a continuous procedure as long as heat is being absorbed by the collector.
Now, since latent heat is being used for heat movement instead of sensible heat, if the load at the heat exchange structure is equal to the heat input at the collector, the pressure in the system will remain constant and not increase. Therefore, the collector plate temperature can remain lower than in old style systems where sensible heat is picked up. Since the .DELTA.T in the collector is greater, the efficiency of a collector can be much greater than for old style collector fluid charged systems.
Also, the response to sudden bursts of sunlight is almost instantaneous in a refrigerant charged system and it will be picking up and transferring usable heat before the old style collector fluid charged system can get started.
Whenever the heat exchange structure is located above the collector, a circulating pump can usually be eliminated. When desired to locate the heat exchange structure below or near the same height as heat pick up, a small refrigerant circulating pump is used. However, since latent heat of the refrigerant is used for heat movement instead of sensible heat, a relatively small weight of refrigerant needs to be circulated and very little power is required.
The present invention comprises a package which may be installed with collectors and the entire system charged with refrigerant for use in heating water.
The use of a refrigerant charged solar system instead of a collector fluid has many advantages, some of which are listed below:
(1) Refrigerant in such a system eliminates forever all worry about freezing because the refrigerant does not freeze.
(2) Also, it eliminates any question as to corrosion or chemical action in the collector or water heating system.
(3) Toxicity is not a problem since most refrigerants are non-toxic.
(4) Refrigerant charged collectors respond faster and are, therefore, more efficient on cloudy days.
(5) A refrigerant charged system is more efficient since basically latent heat is used instead of sensible heat as in the case of the collector fluid. This, in many cases, results in the heat being moved through smaller lines and longer distances without expenditure of energy to run a pump.
(6) In many cases, a primary circulating pump can be eliminated and a very efficient passive system can result.
(7) Low grade heat for use with heat pumps may be more readily picked up with a refrigerant charged system.
(8) Refrigerants are readily available and some collector fluids are not. The cost is usually less when charging with a refrigerant since refrigerants are produced in high production and are readily available and fewer pounds are used because the system is not flooded.
(9) It is relatively easy to find leaks in a system charged with refrigerant since a conventional leak detector may be used.
(10) A heat exchanger in a refrigerant charged system is more efficient since the temperature remains a maximum throughout the heat exchanger chamber. Both inlet and outlet are at the same temperature while in a liquid to liquid heat exchanger this varies throughout.